1. Field
The present disclosure relates to optical scanning devices and more particularly to a new and improved laser scanning assembly having an improved angle multiplication factor.
2. Brief Description of the State of the Art
In many laser scanning bar code symbol readers, employing multi-line laser scanning patterns, a faceted mirror with a set number of sides facing generally different directions (i.e. a polygon) is used as the scanning element.
However, a disadvantage of the polygon scanning element employed in such prior art scanning systems is that the achievable sweeping scan angle of a laser beam reflected off of such a scanning polygon can be no greater than two times the angle of rotation, and is usually less than two times. Also, in order to approach the limiting factor of two, the incident laser beam as well as the normal vectors to the mirror surfaces must be nearly perpendicular to the rotation axis. This prevents the laser beam from sweeping through a full 360 degree circle. To achieve a full circle of coverage with a single beam, the beam needs to be parallel to the rotation axis, with a single rotating mirror angled near to 45 degrees, but this reduces the maximum scan multiplication factor from two to one.
Additionally, traditional rotating polygons, with a scan multiplication factor near two, experience a loss of light collecting ability as they rotate away from a point of symmetry due to the narrowing of the apparent width of the mirror as it rotates. This happens if the polygon mirror is the limiting light-collection aperture of the system, which can be difficult to avoid in a traditional system design.
And while U.S. Pat. No. 5,177,347 discloses a polygon-based laser scanning system, in which a pair of rotating mirrors are used with a stationary cluster of mirrors, this laser scanning configuration does not amplify the scan angle multiplication factor of the pair of rotating mirrors beyond two, nor does it provide circular coverage.
Thus, there is great need in the art for a new and improved laser scanning assembly that is capable of generating a laser scanning pattern while amplifying the scan angle multiplication factor of the rotating mirrors beyond two, and thereby avoiding the shortcomings and drawbacks of the prior art scanning methods and apparatus.